Electrodeposition of nickel



United States Patent ELECTRODEPOSITION 0F NICKEL Henry Brown, Huntington Woods, Mich, assignor to The Udylite Research Corporation, Detroit, Mich, a corporation of Michigan No Drawing. Application April 5, 1054, Serial No. 421,180

20 Claims. (Cl- 204-49) The present invention relates to the electrodeposition of nickel from an aqueous acidic bath, and more particularly relates to the production of nickel plate having superior ductility, and brightness in comparison to that of heretofore known nickel plate.

It is now old in the art to employ a single organic compound to yield a semibright nickel deposit as is taught in U. S. Patent 2,026,718, or to use a combination of organic compounds to yield a full bright nickel deposit as set forth, for example in U. S. Patent 2,321,182. It has been suggested in U. S. Patent 2,635,076 that ductile nickel plate having a bright appearance may be produced from aqueous acidic nickel plating baths by adding to such baths coumarin or certain derivatives of coumarin. The derivatives of coumarin which are said to be suitable include coumarins which have one or more of the replaceable hydrogen atoms replaced by an alkyl, acyl, chloro, hydroxy or carboxy group. Certain disadvantages have been found to exist when attempts are made to operate aqueous acidic nickel plating baths containing such additives including the formation of oily products in the bath which cause streaks and bunched pits in the plate and the relatively rapid build-up of cathode decomposition products which require periodic removal by carbon treatment of the bath or the equivalent of such treatment.

It has surprisingly now been found that it is possible to produce fine-grained lustrous nickel deposits from the Watts type of nickel bath or its modifications while concurrently avoiding the disadvantages which accrue from the use of coumarin or the heretofore suggested derivatives of coumarin, by the addition to such baths of certain mono-alkoxy coumarins as set forth more completely in Table III. The presence of these alkoxy coumarins, namely alkoxy coumarins having not more than two carbon atoms in the alkoxy group and being positioned on the coumarin nucleus in a position numbered at least as high as 6 by conventional nomenclature, in the bath causes the plate which is electrodeposited therefrom to be very fine-grained even though it may be cloudy and milky in appearance, and to show marked increasing luster with continued plating. The 6-, 7-, or 8-position substituted mono-methoxy or mono-ethoxy coumarins impart exceptional luster and marked increasing luster with increased thickness of nickel plate when used alone in the warm acidic nickel baths of the Watts type and similar types. That is, the improvement in luster and brightness and the marked increasing luster and brightness with increased thickness of nickel-plate is amazing when compared to other substituted coumarins, for example, hydroxy coumarins (7-hydroxy coumarin, i. e., umbelliferone of U. '8. 2,635,076, April 14, 1953) or, for that 'matter,- carboxy coumarins, or chloro, or methyl substituted coumarins. The improvement is. greater than formaldehyde (n-( i-H) compared with hydroxy-formaldehyde Patented June 11, 1957 i. e. formic acid) in the nickel bath and is as important as the amazing and exceptionalditference between maleic acid compared to dimethyl maleate, or acrylic acid compared to methyl acrylate, or aconitic acid compared to trimethyl aconitate, where in these cases the unsaturated carboxylic acids are actually harmful in the nickel bath (cause darkish plate-with no marked brightness when used in conjunction with the benzene sulfonimides, sulfonamides and sulfonic acids), while the esters are very beneficial in causing high luster and brilliance. Furthermore, these methoxy and ethoxy substituted coumarins are an improvement over coumarin itself. Moreover the 6-, 7- or 8-mono-methoxy or mono-ethoxy coumarins do not cause oily efiects (streaks and bunched pitsin the nickel plate) in the nickel baths operated-at temperatures of from 60 C. to C. even when concentrations higher than about 1 gram per liter are used. Furthermore, the cathode reduction product formed during plat ing from baths containing the additives of this invention is much less harmful to the nickel plate than that formedwith coumarin or the hitherto suggested derivatives of coumarin in the bath, and for this reason nickel plating baths containing the alkoxy coumarins of this invention require carbon treatment less often, and give brighter plate.

It has also been found that brilliant, highly lustrous nickel plate having good ductility is obtained when the alkoxy coumarins of this invention are used in conjunc tion with a material containing another different functional group, viz., the unsaturated methylene sulfone group,

as emplified by benzene sulfonic acids, benzene sulfonamides and sulfonimides. The presence of the alkoxy coumarins of this invention alone in a Watts type nickel bath or the presence of a material containing the unsatu-' rated methylene sulfone group alone gives no obvious indication of the remarkably different and enhanced result which occurs when both materials are concurrently present. The superiority of baths containing conjointly both materials relative to increased brightness and rate of brightening is particularly pronounced and apparent in comparison to baths containing the chloro or methyl or hydroxyl or carboxyl substituted coumarins, and to coumarin.

While the simpler aryl sulfonamides and some of the aryl sulfonic acids produce bright and mirror-like deposits on bufied metals such as buffed brass, these com-' pouiids fail to accomplish the same result on steel which is polished, for example, with 200 emery paper or where the nickel is plated on top of matte (but unburnt) copper plate of 0.003" to 0.0005" thickness, and yield in these cases plate of dull and grey appearance. If, however, one of these alkoxy coumarins and a material containing the unsaturated methylene sulfone group are used together, a brilliant mirror-like deposit can be obtained even on a matte copper deposit. When the 6-, 7-, or S-methoxy coumarins are used in combination with the benzene sulfonamides of sulfonimides, an increased rate of brightening in the middle current density ranges may be obtained by adding to the bath a small amount of about 0.001 gram/liter to 0.4 gram/liter of one of the compounds of Table l of United States Patents 2,647,866, 2,648,628 and 2,654,704.

The aryl sulfones (sulfonamides, sulfonic acids), in general do not have a critical concentration range in the bath, and they produce practically no further improvement after their optimum concentration is reached. In the case of an alkoxy coumarin of' Table III, there is preferential reduction of the unsaturated compound with respectto the nickel ion, whereas with the aryl sul-.

' tones, the nickelion is reduced preferentially. The vari ation Qfth-e reduction with the variation of the potentials between adjacent high and low points will account for the rate of brightening or smoothening out effect.

The concentration of'the methoxyand ethQxy-coumarins which may be advantageously employed is not critical in any concentration up to saturation and these materials may be used at concentrations between about 0.05 gram per liter to about 2 grains/liter, the preferred concentrationbeing 0.1 gram/liter.to 1.0 gram/liter.

The best cathode .film buffer is boric acid and it is important to keep its concentration high (over 30 grams/ liter), especiallyin the warm baths. Other buffers may beu sed preferably in small amounts (1 to 5 grams/liter) with the boric :acid withr-beneficialjeifects, such as formic, citric, fiuobor ic acids, etc., but they are not recommended to be used alone, except in the caseof nickel fiuoboratc for high speed plating.

Inthe-use of the alkoxy conmarins alone in the bath, or in the presence of the benzene sulfonic acids, sulfonamides and sulfonimides (sulfimides), ammonium salts should be kept at a minimum. The concentration of zinc and copper ions in the bath should also be kept as low as possible. This is especially desirable where the concentration of benzene sulfonic acids or-benzene sulfonamides is low in the bath or the latter compounds are absent.

.Soft, sulfur-free plate and increased brightness, especially in the middle current density range may be obtained by using an admixture of the 6-, 7- or 8-methoxy or ethoxy coumarin in an amount between about 0.05 gram/liter to saturation with about 0.05 to 0.4 gram/ liter of at least one of the group consisting of chloral hydrate, bromal hydrate .and formaldehyde.

The baths may be operated at pH values ranging from 2.0 to 5.5 and temperatures ranging from 20 degrees C. to 70 degrees C. and even higher, and the preferred current density ranges may be from 5 to l50-amps./sq. ft. depending on the agitation, the temperature of the bath and the concentration and the type of nickel salts. The 6-, 7- or S-methoxy or ethoxy coumarins of this invention function better at the higher pH values of the nickel bath, that is, 3.0 to 5.5 and the best operating range has been found to be between about 4.2 and 4.5. One of the important advantages of the methoxy and ethoxy coumarins of this invention resides in their ability to function in the lower pH range of 3.0 ton-3.5 in comparison to heretofore known high leveling baths which usually require a pH of 4.0 to 4.5. At these lower pH values the precipitation of ferric hydroxide is avoided which in the higher pH baths results in roughness and pitting unless a very rapid rate of filtration is employed. The benzene sulfonamides and sulfonimides may be used etfectively in concentrations of from 0.05 gram/liter to saturation.

In Table I are listed preferred bath compositions.

TABLE I N18 04.61120, NlC1z.6H20, H33 03, Temp. Optimum,

-l -l al t D In Table II are listed representative examples of the p mumco grams/liter 6-chlor o-benzoyl sulfimide 0.1-1 M-aldehydo benzene sulfonamide 0.1-1 Sulfomethyl benzene sulfonamide 0.1-6 Benzene sulfonamide m-carboxylic amide 0.1-3 7-aldehydo o-benzoyl sulfimide 0.1-3 N-acetyl benzene sulfonimide 0.1-2 Methoxy benzene sulfon'amides 0.1-1 Hydroxyrnethyl benzene sulfonamide 0.1-2 p-Carboxylic amide benzene sulfonamide 0.1-3 p-Chlor benzene sulfonamide 0.1-3 Benzene mono, dior tri-sulfonic acid l-10 TABLE III Optimum Alkoxy. Goumarins Cone,

.. grams/liter 6-, or 7-, or S-Methoxycoumarin 0.1-2 6-, or 7-, or 8-Ethoxycoumarin;..; 0.,1-2

Examples of specific baths which are suitable for the purposes of this inventionware given below.

Example v1 NiClz.6H2O grams/1iter HBBO? (in 45.59 8-methoxyc do -0.1-0.6 pH i 3.8-4.8 Temperature F Example 2 NiClz.6H2O grams/1iter NiSO45H2O do 150 HsBOa do 40 Ni(BF4)2 l-6 7-methoxycoumarin do 0.3-2 o-Benzoylsnlfimide do 0.1-0.5 Benzene sulfonamide a '1 2 H V p V 3.0-4.5

Example 3 NiSO4.6HzO "grams/liter" 200-300 NiCl2.6H2O do 40-75 HsBOa "do"-.. 40 8-rnethoxyco1unarin do 0.l-0.2 Chloral hydrate do 0.1-0.2 P V 3.0-4.5 Temperature F 110-140 Example 4 NiS04.6HzO grams/ 1iter 200-300 Niflo d-o 40-75 H3Bna dO .40 Ni(BF4)2 do .14 S-methoxycoumarin do 0.3-1.5 o-Benzoyl sulfimide do L 0.1 03 P AM:

Example 5 NiCl2.6H2O g-rams/liter 100 H3303"- do i 40 S-ethoxycoumarin do 0.3-1 Benzene sulfonamide; do i1-2 Example .6

NiSO4.6HzO ...-grams/liter 200-300 NiC12.6HzO do 40-75 HsBOw r 04-.. 40 8-ethoxycoumarin Q do 0.3-1 o-Benzoyl sulfimide ....d0..- 0.1-1

Example 7 V Nicnsrno grams/liter.... 100 HsBO do 45-50 7-methoxycoumarin (in (1144 H 3.8-4.8 Temperature F 140 Example 8 NiCl2.6Hz0 "grams/liter" 100 H3BO3 do 45 8-methoxycoumarin do 0 1 0 pl-I 4.2

Example 9 NiClz.6I-I2O grams/liter 100 H3BO1 dn 45 8-eth0xycoumarin -c do 0.1-0.2 pH 4.2 Chloral hydrate grams/liter -0.1-0. Temperature F.. 110-140 Example 10 NiCl2.6H2O ....-grams/liter 100 HsBO dn 45 8-methoxycoumarin 'do 0.1 Chloral hydr do 0.1-0.2 Formaldehyde do .05-0.1 H 3.8-4.5 Temperature F 115-140 Example 11 NiSO4.6H2O ..grams/1iter 100 NiCl2.6H2O .do 100 HsBOs d 45 S-ethoxycoumarin do 0.1 Di(methyl Cellosolve) maleate do 0.5 Chloral hydat d 0.1 pl-l' 3.8-4.5 Temperature F 115-140 Of exceptional performance are Examples 2, 4, 6, as full bright nickel plating baths yielding ductile high leveling deposits, superior to any hitherto known derivative of coumarin and of coumarin itself in combination with the compound. The superiority lies not only in the brighter plate obtained from the standpoint of the fast rate of brightening, but also in the wider range of current density over which the rate of brightening is superior (especially the middle and lower current densities in which coumarin and its hydroxy, alkyl and carboxy derivatives are poor), and the lower frequency of needing activated carbon treatments. For the softer semi-bright (cloudy lustrous) deposits, chloral or bromal hydrate in a concentration of 0.1-0.2 gram per liter is a distinct advantage in conjunction with any coumarin derivative. Very small amounts of formaldehyde (0.05-0.2 gram/liter) in conjunction with the chloral hydrate or bromal hydrate as pointed out in U. S. 2,321,182 is also beneficial in obtaining smooth fine-grained ductile plate from the baths containing an alkoxy coumarin of this invention. Furthermore, the semi-bright (cloudy lustrous) plates obtained from the chloride-type baths containing the aldehydes as well as the alkoxy coumarin as in Examples 9 and 10, can be most safely transferred to full bright nickel baths without loss of adhesion compared to Watts type baths.

Also in nickel baths containing the alkoxy coumarins of this invention, the addition of trimethyl aconitate (0.1-1 gram/liter) or di(methyl Cellosolve) maleate (0.1-1 gram/liter) as well as the chloral hydrate (0.05- 0.2 gram/liter), results in obtaining smooth fine-grained ductile plate over longer periods of operation without the 6 necessity of activated carbon treatments or similar purification treatments to remove electrolytically formed break-down products.

While 6-, 7- and 8-alkoxy coumarins have been specifically discussed hereinabove, 5-alkoxy coumarin is also intended to be included although the 5-alkoxy coumarins are more ditli-cult to prepare.

What is claimed is:

1. A bath for electrodepositing lustrous nickel comprising an aqueous acidic solution consisting essentially of an electrolyte selected from the group consisting of nickel sulfate, nickel chloride and mixtures thereof in the presence of an alkoxy coumarin having not more than 2 carbon atoms in the alkoxy group, said alkoxy group being in a position on the coumarin nucleus numbered at least as high as 5, said alkoxy coumarin being present in the amount of about 0.05 gram/liter to saturation.

2. A bath as claimed in claim 1 wherein the alkoxy coumarin is S-methoxy coumarin.

3. A bath as claimed in claim 1 wherein the alkoxy coumarin is 7-methoxy coumarin.

4. A bath as claimed in claim 1 in which the alkoxy coumarin is 6-methoxy coumarin.

5. A bath as claimedin claim 1 wherein the alkoxy coumarin is 8-ethoxy coumarin.

6. A bath as claimed in claim 1 wherein the alkoxy coumarin is 7-ethoxy coumarin.

7. A method for electrodepositing bright nickel consisting of electrodepositing nickel from an aqueous acidic nickel solution consisting essentially of an electrolyte selected from the group consisting of nickel sulfate, nickel chloride and mixtures thereof in the presence of an alkoxy coumarin having not more than 2 carbon atoms in the alkoxy group, said alkoxy group being in a position on the coumarin nucleus numbered at least as high as 5, and being present in an amount of about 0.05 gram/liter to saturation.

8. A method as claimed in claim 7 wherein the alkoxy coumarin is 8-methoxy coumarin.

9. A method as claimed in claim 7 wherein the coumarin is 7-methoxy coumarin.

10. A method as claimed in claim 7 wherein the alkoxy coumarin is 6-ethoxy coumarin.

11. A bath for electrodepositing lustrous nickel comprising an aqueous acidic solution consisting essentially of an electrolyte selected from the group consisting of nickel sulfate, nickel chloride and mixtures thereof in the presence of an organic compound dissolved in the aqueous acidic nickel solution in a concentration of alkoxy about 0.05 gram/liter to saturation and selected from the 7 group consisting of benzene sulfonic acids, sulfonamides and sulfonimides, and about 0.05 gram/liter to saturation of an alkoxy coumarin having not more than 2 carbon atoms in the alkoxy group, said alkoxy group being in a position on the coumarin nucleus numbered at least as high 5.

12. A bath as claimed in claim 11 wherein the alkoxy coumarin is S-methoxy coumarin.

13. A bath as claimed in claim 11 wherein the alkoxy coumarin is 7-methoxy coumarin.

14. A bath as claimed in claim 11 wherein the alkoxy coumarin is 6-methoxy coumarin.

15. A bath as claimed in claim 11 wherein the alkoxy coumarin is 8-ethoxy coumarin.

16. A bath as claimed in claim 11 wherein the alkoxy coumarin is 7-ethoxy coumarin.

17. A bath for electrodepositing lustrous nickel comprising an aqueous acidic solution consisting essentially of at least one nickel salt selected from the group consisting of nickel sulfate and nickel chloride, in the presence of about .05 gram/liter to saturation of an alkoxy coumarin having not more than 2 carbon atoms in the alkoxy group, said alkoxy group being in a position on the coumarin nucleus numbered at least as high as 5, and

about 0.05 to about 0.2 gram/liter of at least one ma- 7 t terial selected from the group consisting of chloral ,hydrate, brornal hydrate and formaldehyde. v

18. A method for electrodepositing lustrous nickel consisting of electrodepositing nickel from an aqueous acidic nickel solution consisting essentially of at least one nickel salt selected from the group consisting of nickel sulfate and nickel chloride in the presence of about .05 gram/ liter to saturation of an alkoxy coumarin having not more than 2 carbon atoms in the alkoxy group, said alkoxy group being in a position on the coumarin nucleus numbered at least as high as '5, and about 0.05 to about 0.2 gram/liter of at least one material selected from the group consisting of chloral hydrate, bromal hydrate and formaldehyde.

19. A bath for electrodepositing lustrous nickel cornprising an aqueous acidic solution consisting essentially of at least one nickel salt selected from the group consisting of niekel'sulfate' and nickelchloride in the presence of about 0.05 gram/liter to saturation of an alkoxy coumarin having not more than two carbon atoms in the alkoxy group, said alkoxy group being in a position on the cournarin nucleus numbered 'at least as high as 5, about 0.05 to about 0.2 gram per liter of at least one material selected from the group consisting of chloral hydrate, bromal hydrate and formaldehyde, and about 0.1 to about 1 gram/liter of at least one material selected from the group consisting of trirnethyl aconitate and di-' (methy C l ow v m t t 20.. A method for electrodepositinglustrous nickel consisting ofelectrodepositing nickel from an aqueous acidic nickel solution consisting essentially of at least one nickel salt selected from the group consisting of nickel sulfate and nickel chloride in the presence of about 0.05 gram/- liter to saturation of an alkoxy cournarin having not more than two carbon atoms in the alkoxy group, said alkoxy group being in a positiqnon thecoumarin nucleus numbered at least as high as 5, about 0,05 to about 0.2 gram per liter of at least one material selected from the group consisting of chloral hydrate, brornal hydrate and formaldehyde, "and about 0.1 .to abouttl gram/liter of at least one material selected from the group consisting of trimethyl aconitate and di(methyl Cellosolve) maleate.

References Cited in the file of this patent 

1. A BATH FOR ELECTRODEPOSITING LUSTROUS NICKEL COMPRISING AN AQUEOUS ACIDIC SOLUTION CONSISTING ESSENTIALLY OF AN ELECTROLYTE SELECTED FROM THE GROUP CONSISTING OF NICKEL SULFATE, NICKEL CHLORIDE AND MIXTURES THEREOF IN THE PRESENCE OF AN ALKOXY COUMARIN HAVING NOT MORE THAN 2 CARBON ATOMS IN THE ALKOXY GROUP, SAID ALKOXY GROUP BEING IN A POSITION ON THE COUMARIN NUCLEUS NUMBERED AT LEAST AS HIGH AS 5, SAID ALKOXY COUMARIN BEING PRESENT IN THE AMOUNT OF ABOUT 0.05 GRAM/LITER TO SATURATION. 